Question

Mark is suffering from an X-linked dominant deafness (P=0.5). His wife is also suffering from the same type of deafness. This couple is pregnant with a boy. What is the chance that this boy would suffer from this type of deafness? First, draw a pedigree for this family and then figure out the correct answer.

a) 100%
b) 80%
c) 50%
d) 40%
e) 25%
f) 20%
g) Zero

Answer 1

The chance that a boy will inherit X-linked dominant deafness from parents who both have the condition is 50%. This is because he has a 50% chance of inheriting the affected X chromosome from his mother and cannot inherit the condition from his father, who passes on the Y chromosome.

Step-by-step explanation:

The student's question is regarding the probability that a boy will inherit X-linked dominant deafness when both parents are affected by this condition. In the case of X-linked dominant disorders, if a male with the disorder (P=0.5) has a child, all of his daughters will inherit the condition because they receive his only X chromosome which has the dominant allele for deafness. However, because males pass on their Y chromosome to their sons, the sons will not inherit the X-linked trait from their father.

The mother, in this case, has the disorder, which means she has at least one dominant allele on one of her X chromosomes. Since the son will inherit one of the mother's X chromosomes, there is a 50% chance that he will inherit the X chromosome with the dominant allele for deafness, and a 50% chance that he will inherit the other X chromosome without the allele. Thus the son's chance of having this type of deafness is 50%.

Based on the given scenario, the correct answer would be c) 50% chance that their son would suffer from X-linked dominant deafness.